With an increase in the degree of integration of semiconductor devices, variation in the height of structures formed on a semiconductor wafer is increasing. In the case where such height variation is high, it is difficult to accurately print a mask pattern due to problems related to DOF (Depth Of Focus) in a subsequent lithography process.
Thus, in order to flatten the surface of a wafer, chemical-mechanical polishing (hereinafter referred to as “CMP”), in which chemical removal processing and mechanical removal processing are combined into a single process, is widely utilized these days.
Typically, a CMP process is performed in a manner in which a wafer surface having varying height is brought into close contact with a polishing pad, and a slurry, serving as a polishing liquid containing an abrasive and a chemical material, is then injected between the wafer and the polishing pad to thus flatten the surface of the wafer. Briefly, CMP is a process of flattening a semiconductor wafer through removal of a certain film therefrom, and in the CMP process, the uniformity of the polished surface after the polishing is regarded as very important.
The construction for CMP includes a head to which a wafer is mounted, a pad rotating in the same direction, and a slurry containing nano-sized polishing particles therebetween, the wafer being mounted to the head by means of surface tension or a vacuum. In the CMP process, a wafer is polished by the pad and the slurry, and a polishing table equipped with the pad performs a simple rotational motion and the head part simultaneously performs both rotational motion and oscillatory motion and presses the wafer toward the polishing table with a predetermined pressure. The wafer surface and the pad come into contact with each other due to the self-load of the head part and the applied pressure, and the slurry, which is the processing liquid, is allowed to flow into fine gaps between the contact surfaces, that is, into pores in the pad. A mechanical removal process is performed by the polishing particles in the slurry and the surface projections of the pad, and a chemical removal process is conducted by the chemical component in the slurry. Also, polishing particles or surface projections come into contact with top of the protruding portion of the wafer on which the device is formed, and pressure is intensively applied to the protruding portion, and thus the protruding portion has a relatively high surface removal rate compared to the other portions. As the processing progresses, protruding portions are uniformly removed over the entire area. During the flattening process, polishing has to be stopped at the layer where a silicon oxide film appears. The CMP process may be classified into a process type in which only the same material is polished during the processing to thus remove only a predetermined thickness and a process type in which a polishing end point is determined while coming into contact with a different kind of material. In the case where the polishing rate of a layer that must not be polished is significantly lower than the polishing rate of a material to be polished during the processing, the polishing end point (PEP) may be naturally determined due to slight over-polishing. Here, the polishing ratio of two materials is referred to as a selectivity ratio. The slurry used in the CMP process is configured such that an abrasive that realizes a predetermined selectivity ratio should be mixed with a solution in an atmosphere that may cause a chemical reaction. Specifically, during the damascene process, there is required a slurry, in which the polishing ratio of two materials is different, that is, the selectivity ratio is different, in a manner in which a silicon nitride film is preferentially polished and polishing is stopped at the time that a silicon oxide film being exposed. Furthermore, there is required a slurry, which causes no damage to a metal layer and improves the electrical properties of a device. However, conventionally developed slurry cannot be used in the damascene gate process because the polishing rate of a silicon oxide film is much higher than that of a silicon nitride film. The effectiveness of the CMP process depends mainly on the properties of the slurry, so the development of an optimal slurry composition for CMP is required.
Meanwhile, the surface to be polished during CMP exposes various kinds of materials, such as a polysilicon film (polycrystalline silicon film), a monocrystalline silicon film, a silicon oxide film, a silicon nitride film, etc. Conventionally, a slurry composition for CMP, which is targeted to any one of the above materials, is used to remove the target material through CMP. However, when the polishing rate of the target material is significantly different from that of another material, the target material is excessively polished, undesirably causing defects such as dishing or erosion. Also, since the processing is carried out in a manner in which a CMP slurry composition suitable for each of the target materials is selected and a removal process is performed through CMP, productivity is lowered, which is undesirable.
With the recent diversification of the structure of semiconductor devices, three kinds of films, namely a polysilicon film, a silicon oxide film and a silicon nitride film, are required to be simultaneously polished. In order to simultaneously polish the three kinds of films, it is necessary to develop a slurry composition, which may perform a polishing process by adjusting the selectivity ratio of the films with the slurry composition alone for CMP, apart from the steps of selecting a slurry suitable for each polishing target and supplying the slurry.
Regarding techniques capable of performing a polishing process by adjusting the selectivity ratio of the films with the slurry composition alone for CMP, Korean Patent No. 1396853 discloses ┌Slurry composition for polishing silicon nitride, method of polishing silicon nitride film using the same, and method of manufacturing semiconductor device┘, in which the slurry composition for polishing silicon nitride enables a silicon nitride film to be polished at a high polishing selectivity ratio relative to a silicon oxide film, and may thus be efficiently applied to the process of manufacturing a semiconductor, which requires selective removal of the silicon nitride film. Also, Korean Patent Application Publication No. 2014-0133604 discloses ⇄CMP composition selective for oxide and nitride having high removal rate and low defectivity┘, in which the CMP composition is composed of a ceria abrasive, one or more nonionic polymers, optionally one or more phosphonic acids, optionally one or more nitrogen-containing zwitterionic compounds, optionally one or more sulfonic acid copolymers, optionally one or more anionic copolymers, optionally one or more polymers comprising quaternary amines, optionally one or more compounds that adjust the pH of the polishing composition, water, and optionally one or more additives, thus exhibiting preferable selectivity of silicon oxide, silicon nitride and/or polysilicon. Also, the method of chemically and mechanically polishing a substrate including silicon oxide, silicon nitride and/or polysilicon using the above CMP composition is disclosed.
Therefore, the present invention is aimed to a slurry composition for CMP, which enables polishing by adjusting the selectivity ratio of the films through control of amounts of an additive and a solvent, without the need to use a separate slurry suitable for each film (a silicon oxide film, a silicon nitride film and a polysilicon film) depending on the polishing target.